A search of the records of the Patent and Trademark Office prior to the preparation of this application failed to develop prior art for armored door openers for field artillery ammunition support vehicles but did develop U.S. Pat. Nos. 2,711,343 and 3,815,950 in Class 296, Subclass 56 showing the use of compression springs in door openers and further developed U.S. Pat. No. 4,094,158 of June 13, 1979 and assigned to the United States of America. This patent relates to a loading gate for mine roof bolter apparatus in which a gate 10 is raised to horizontal position by an hydraulic cylinder 51 acting on a pivoted arm 38 connected to the door by link 40 to hold the door either in raised position or in fully closed position with the door in raised position acting as a crew shield. The door actuater of this patent requires hydraulic power to drive the piston in cylinder 51 to either open or close the door and the door cannot be raised or lowered manually. In this patent, when the door is closed the pivots are not aligned for security and an over-the-center arrangement is required between the arms 40 and 38 to assure locking of the door in raised position.
The present invention provides the advantages of manual actuation of a very heavy armored door either to fully raised position or to closed position without danger to the operator and with substantially all of the weight of the door compensated for by the arrangement of the compression spring and pivots which are aligned when the door is closed so that no opening force is applied to the closed door although the springs are at maximum compression. With this arrangement, as the door begins to open the spring pivot points become slightly offset from the fixed pivots providing sufficient force to further open the door. This offset increases as does the opening force until the door is horizontal or substantially horizontal. No hydraulic power is required for opening or closing the door .